The present invention relates to a process and a device preventing the skidding of vehicles on the road. In this case, the term "vehicle" can be a means of transportation driven by an engine, such as an automobile, as well as a non-driven vehicle, such as a towed trailer. The skidding motion referred to in the present case is neither a lateral drift perpendicular to the direction of travel, nor a push with blocked tires in the direction of travel, but an involuntary rotary motion around the vertical axis of the vehicle that is not determined by the position of the tires.
This skidding motion can be caused by one of the following:
It can be the result of an intended change of direction in which the vehicle is travelling. This requires the transmission of lateral forces by the tires onto the vehicle. If it exceeds the adhesive limit of the tires, the vehicle will ideally drift in a lateral direction. In most cases, the adhesive limit will not be exceeded at both axes simultaneously. This will lead to a rotary motion and, thus, skidding of the vehicle.
A further cause for skidding are suddenly occurring lateral forces, such as the ones caused by gusty winds.
Another cause for skidding are the more or less frequent vibrations of the vehicle itself that, in turn, are initiated by occasional irregularities in the road surface.
Moreover, skidding can be caused by asymmetrical drive and brake actions especially in case of reduced limiting friction.
The skidding process has a positive reaction characteristic, i.e. a small initial disturbance will result in a change in direction, which will, in turn, trigger a larger disturbance that can, ultimately, result in a continuous series of vibration. This will cause the driver, especially one lacking experience, to lose control over the vehicle. It is, therefore, advantageous to eliminate any disturbance in its initial stage.
There are numerous devices that have been recommended for the prevention of skidding. One of them is the Anti-Blocking-System (ABS) that is successfully used in vehicular technology. In the ABS, the rotary speed of the individual wheel is compared to the vehicle speed with a difference in both speeds indicating the loss of contact with the road. An automatic system will then change the drive and brake effect at this wheel and, thus, restore the lost contact with the road. The ABS is a passive system in that it cannot neutralize the disturbing forces by means of compensative counter-forces.
Other devices attempt to actively compensate for any disturbing forces suddenly impacting the vehicle. The simplest form of such a compensation is an easily moveable mass that is linked to the vehicle mass by means of springs in the preferred direction in which a disturbance will take effect. The spring characteristic is chosen in such a way that it will preferably compensate for vibrations within a certain frequency range. In U.S. Pat. No. 4,687,225, such a moveable mass is used between two springs in a housing that is partially filled with liquid and it is recommended to install this housing close to the rear axle. A similar recommendation for the prevention of self-induced vibrations in trailers is also mentioned in DE Pat. No. 28 07 972 A1.
In another recommendation according to EP Pat. No. 0'098'657, such a spring-loaded mass can also be replaced by a flywheel. Due to the kinetic energy of the flywheel, the stabilizing counter-forces can be generated by a smaller mass.
Other systems that have been recommended include some that determine the disturbing forces with the help of an accelerometer with regard to strength and direction and use a power-assisted control system to generate a counter-force determined by the measured direction and strength. U.S. Pat No. 3,909,044 proposes a system in which a rotary system is used for the detection of lateral forces impacting a trailer. In this instance, the counter-force is generated by the towing vehicle by using a brake assembly to reduce the usually swiveling connection between towing vehicle and trailer in its movability as a function of the strength of the disturbing force.
U.S. Pat. No. 4,200,168 describes a system for the stabilization of swinging motions in a vehicle in which a detection system, in form of a physical pendulum, determines the strength and direction of a disturbance and, by means of a hydraulic relay, converts it into a pressure flow that, in turn, causes a corresponding motion in a flywheel by means of a hydraulic engine. The acceleration of this flywheel generates a torque directed against the disturbance. This device is particularly recommended for one-track vehicles and the acceleration process can also be used to move a mass that will improve the mass-center position of the inclined vehicle.
FR Pat. No. 2,606,110 describes a more elaborate system using four flywheels in one common plane of which two are arranged symmetrically right and left on a plane perpendicular to this plane and rotate in the opposite direction, while the disturbing forces take effect along this vertical plane. Frequency, amplitude, and phase of a vibrating disturbance are analyzed by an accelerometer and subsequently converted into an electric signal by means of a computer. This signal will then be compared to signals corresponding with the speed and position of the electric motors driving the flywheels. The difference results in a control signal supplying each motor with the corresponding voltage so that the combined effort of the four flywheels compensates for the disturbing torque.
The skidding reaction of vehicles has already been dramatically improved by the use of the ABS technology, especially in case of extreme changes in speed on roads with reduced limiting friction as is the case when a braking action is performed on a wet or icy road. Even the propagation of a continuous skidding-vibration reaction is reduced. The ABS system is, however, a passive system in that it cannot generate any active counter-forces in case of disturbing forces, but only optimize the limiting friction of the vehicle with regard to the road. Such passive systems are of only limited use, particularly in case of suddenly occurring disturbances, since they fail to compensate these occurring disturbing forces.
The disadvantage of the active systems mentioned above is the fact that the additional mass needed for the generation of sufficient counter-forces increases the total weight of the vehicle in an undesirable manner (U.S. Pat. No. 4,687,225, DE 28'07'972 A1, EP 0'098'657) and allows only for the compensation of periodic disturbances within a very limited frequency range for which these damping systems have received optimum adjustment. Most of these proposals are, therefore, dealing to the prevention of skidding in trailers (U.S. Pat. No. 3,909,044) or one-track vehicles (U.S. Pat. No. 4,200,168).
The disadvantage of the system described in FR 2'606'110 is the fact that not all data relevant to determining the rotary condition of the vehicle are measured and, thus, only vibrating disturbances are analyzed and compensated for by means of the flywheels.
The present invention is directed to providing a device and a process that prevents the skidding of vehicles, allows for the active compensation of all disturbing forces occurring at the vehicle with integration of all data relevant for determining the rotary condition of the vehicle (especially if these disturbances are of sudden nature), without increasing the weight of the vehicle to any noticeable extent.
The solution to this problem is presented in the introductory part of patent claim 1 regarding the process and in the introductory part of patent claim 11 regarding the device.
An analysis of the skidding process illustrates the fact that the skidding is caused by a disturbing torque impacting the vehicle which, in turn, causes the current wheel position to deviate from the direction of travel. This is evidenced by the fact that the actual rotary acceleration of the vehicle along its vertical axis does not correspond with the rotary acceleration that should be the result of the turn angle of the wheels, the vehicle speed as well as the change per unit time of these values. An estimated calculation shows that the torques required for the compensation of disturbances are rather small even in a big car and that relatively small torques in the opposite direction suffice in the prevention of the skidding process. This is a classical stability problem: due to the positive feedback quality of the process, it is advantageous to eliminate the disturbance in its early stage.
The process or the device of this present invention does not only measure the actual rotary acceleration of any vehicle along its vertical axis, but also includes the vehicle speed and the position of the steering wheel. The measurements of the last two values serve for the computation of the nominal rotary acceleration with a computer. The difference between nominal and actual rotary acceleration is converted into a control signal. This signal is used to decelerate two flywheels rotating in the horizontal plane of the vehicle in a contra-rotating manner at high speed in such a way that the torque resulting from this deceleration process compensates for most of the disturbing torque which will prevent the skidding process at a relatively early point in time.